Certain power converters are configured to convert direct current (DC) to alternating current (AC). Such DC-AC converters are commonly referred to as inverters. Inverters have many industrial and commercial uses including, for example, converting DC power from a battery or photovoltaic source into AC power for a load. Inverters may also be used to supply AC power to an electric utility grid. A grid-tied inverter is a power inverter that converts direct current (DC) electricity into alternating current (AC) with an ability to synchronize to interface with a utility line. The applications for such an inverter include converting DC sources, such as solar panels or small wind turbines, into AC for tying with the grid. Photovoltaics (PV) in, for example, the aforementioned solar panels generate electrical power by converting solar radiation into direct current electricity using semiconductors that exhibit the photovoltaic effect.
Certain inverters are commonly configured to operate without a transformer. Examples of such inverters are disclosed in Salmi, et al., “Transformerless Microinverter for Photovoltaic Systems”, pp. 639-650, vol. 3, issue 4, Int'l Journal of Energy and Environment (2012); Reddy et al., “Analysis and Modeling of Transformerless Photovoltaic Inverter Systems”, pp. 2932-2938, vol. 3, issue 5, Int'l Journal of Modern Engineering Research (2013); and Dreher et al., “Comparison of H-Bridge Single-Phase Transformerless PV String Inverters”, 10th IEEE/IAS Int'l Conference on Industry Applications, pp. 1-8 (November 2012).
Photovoltaic (PV) power supplied to a utility grid is increasing in popularity as the world's power demands are increasing. Solid-state inverters have been shown to be an important technology for coupling PV systems into the grid. Integration of PV power generation systems in the grid plays an important role in supplying electric power in an environmentally-friendly manner. A commonly-configured grid-connected PV system comprises of a PV panel, and a DC/AC Inverter that is operatively connected to the grid. This configuration is used for power generation in places or sites accessed by the electric utility grid. Depending on the application and requirements, a PV system can either be a stand-alone or hybrid system. Generally the PV system comprises of a PV generator which is a set of series-parallel electrically interconnected solar panels. PV panels are commonly rated in terms of a nominal peak power of the panel at standard test conditions (STC). A PV generator provides the total installed power, which is the sum of nominal peak power of each solar panel present in the PV installation. This PV generator is connected to an inverter which is, in turn, connected to an AC/DC load and/or grid.
Inverters are important components to grid-connected PV systems and their major role is to convert DC power into AC power. Furthermore, inverter interfacing PV module(s) with the grid ensures that the PV module(s) is operated at the maximum power point (MPPT). Based on the photovoltaic arrays' output voltage, output power level and applications, the photovoltaic grid-connected system may adopt different topologies. The grid-connected inverter may be designed for peak power and may obey conditions related to issues like power quality, detection of islanding operation, grounding, MPPT and long-life. Inverter maximum power is typically referred to the total installed power of the PV generator, and should optimize the energy injected to grid. Inverter PV topologies may include centralized inverters, string inverters, multi-string inverter and module inverters.
Although the foregoing discussion focuses particularly on PV systems, those skilled in the art will appreciate that issues that arise in PV systems similarly arise in other contexts that require power conversion/inversion. Such contexts include, but are not limited to, sine wave generating inverters, micro-inverters, power supplies, and power distribution systems.
A significant one of these issues with conventional power inverters is that they carry excessive noise in the output signal. Therefore, improvements to inverter noise control, and accordingly efficiency, are needed in the art.